It is a long-standing objective of color photographic origination materials to maximize the overall response to light while maintaining the lowest possible granularity. Increased photographic sensitivity to light (commonly referred to as photographic speed) allows for improved images captured under low light conditions or improved details in the shadowed regions of the image. In general, the overall light sensitivity provided by the light sensitive silver halide emulsions in such systems is determined by the grain size of the emulsions. Larger emulsions capture more light. In color photographic elements, upon development, the captured light is ultimately converted into dye deposits which constitute the reproduced image. However, the granularity expressed by these dye deposits is directly proportional to the grain size of the silver halide emulsion. Thus, larger silver halide emulsion grains have higher sensitivity to light but also lead to higher granularity in the reproduced image. It has been a long-standing problem to provide materials which maximize the response to light of a silver halide emulsion for any given grain size.
It is of particular interest to find solutions to this problem for large emulsions with the potential for providing high speed (preferably ISO 400 or greater) color photographic materials. Such high speed materials have a number of potential applications. They are particularly valuable for use in cameras with zoom lenses and in single use cameras (also called "film with lens" units). Zoom lenses generally have smaller apertures (higher f-numbers) than comparable fixed focus lenses. Thus, zoom lenses, while giving increased flexibility in composition of a pictorial scene, deliver less light to the camera film plane. Use of high speed films allows the flexibility of zoom lenses while still preserving picture taking opportunities at low light levels. In single use cameras, lens focus is fixed. Here, high speed films allow use of a fixed aperture having a higher f-number, thus increasing the available depth of field, an important feature in a fixed focus camera. For single use cameras with flash, higher film speed allows pictures to be taken with a less energetic flash, enabling more economical manufacture of the single use unit.